System and method for calibrating an irrigation system

ABSTRACT

A system and method for calibrating an irrigation system to account for variations in flow rates caused by field elevation changes, pipe friction losses, water emitter nozzle wear, pressure-regulator inaccuracies, and other factors. A calibration map is created to account for the flow rate variations and then consulted to control operation of the irrigation system.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to agricultural irrigation systems. Moreparticularly, the invention relates to a system and method forcalibrating an irrigation system to account for variations in water flowrates from the irrigation system.

2. Background

Agricultural irrigation systems such as central pivot and lateral moveirrigation systems are commonly used to irrigate crops. A central pivotirrigation system typically includes, among other things, a centralpivot communicating with a pressurized water supply and a main sectionthat moves about the central pivot to irrigate a circular orsemi-circular field. The main section includes a number of mobilesupport towers connected to the central pivot and to one another bytruss-type framework sections. The mobile support towers are supportedon wheels that are driven by a motor on each tower. A water distributionconduit is supported by the framework sections, and a number ofsprinkler heads, spray guns, drop nozzles, or other water emitters arespaced along the length of the conduit for irrigating crops below theirrigation system. Lateral irrigation systems are similar except theydon't include central pivots and move in a relatively straight linerather than a circle.

It is desirable to monitor and control the amount of water delivered byan irrigation system to prevent over or under-watering of crops and toconserve water. Similarly, it is often desirable to deliver differentamounts of water to different portions of a field to accommodatedifferent soil conditions, types of crops, and the existence of roads,boundaries, etc. in the field. Thus, it is common to divide a field intosections and to create an irrigation plan that calls for prescribedamounts of water to be delivered to each section. A control system thencontrols the speed of the mobile towers and/or the opening and closingof water valves to deliver the prescribed amounts of water to eachsection.

Unfortunately, even when following irrigation plans, irrigation systemsoften fail to accurately deliver prescribed amounts of water becausefield elevation changes, water pipe friction losses, water emitternozzle wear, pressure-regulator inaccuracy, and other factors can causevariations in water flow rate, especially over time. Irrigation plansare typically created for expected flow rates from an irrigation systemwhen its on flat, level ground and therefore may call for too littlewater as the irrigation system travels up a hill (and water pressuresdrop) and too much water as the irrigation system operates in a valley(and water pressures increase). Moreover, irrigation plans are typicallycreated when an irrigation system is first placed into service andbecome less accurate over time as pipes, valves, pressure regulators,water emitters and other components age.

SUMMARY

The present invention solves the above described problems by providing asystem and method for calibrating an irrigation system to compensate forvariations in flow rates caused by field elevation changes, pipefriction losses, water emitter nozzle wear, pressure-regulatorinaccuracies, and other factors. In general, the invention first createsa calibration map to assess and record the above-described flow ratevariations and then controls operation of the irrigation system inaccordance with the calibration map to more accurately compensate forthe flow rate variations.

To create a calibration map, actual flow rates through the irrigationsystem, or portions of the irrigation system, are periodically orcontinuously measured and recorded as the irrigation system moves acrossa field. These measured flow rates are then compared to expected flowrates through the irrigation system, or portions of the irrigationsystem, based on the original design or configuration of the irrigationsystem. Correction factors that account for the differences between themeasured flow rates and the expected flow rates are then created fordifferent portions or sections of the field. For example, if themeasured flow rate in a first section is 5% less than expected, acorrection factor of +5% is assigned to that section to indicate 5% morewater is required. Similarly, if the measured flow rate in a secondsection is 10% more than expected, a correction factor of −10% isassigned to that section to indicate 10% less water is required. Thecorrection factors and positional information for the correspondingfield sections are then stored in the calibration map.

The calibration map may be created while the irrigation system isoperating in a calibration mode or “on-the-fly” while the irrigationsystem is irrigating a field. The calibration map may be created whenthe irrigation system is first placed into service and may beperiodically or continuously updated to account for changing conditionssuch as degradation of the valves, water emitters, pressure regulatorand/or other components of the irrigation system.

Once the calibration map is created, a control system consults thecalibration map to adjust at least one operational aspect of theirrigation system in accordance with the correction factors. Forexample, if an irrigation plan or an initial setting of the irrigationsystem calls for 10 gallons per minute (G.P.M.) of water in a section ofthe field, but the calibration map indicates a +10% correction factorfor that section, the control system adjusts an operational aspect ofthe irrigation system so as to apply 10% more water than it would havewithout the calibration map. The operational aspect that is adjusted maybe the speed of the irrigation system's mobile towers, a duty cycle ofthe irrigation system's water emitters, a water flow rate of individualwater emitters or banks of water emitters, or anything else thatcontrols the rate of fluid flow of the irrigation system to adjust waterflow rates in accordance with the correction factors. For example, thecontrol system may operate the mobile towers 10% slower than called forby an irrigation plan so as to apply 10% more water.

One particular embodiment of the invention is a method of calibrating anirrigation system having a plurality of mobile towers and a plurality ofwater emitters supported by the mobile towers. The method comprises:operating the mobile towers to move the irrigation system over a groundsurface; toggling the water emitters as the irrigation system moves overthe ground surface; determining positions of the irrigation system asthe irrigation system moves over the ground surface and as the wateremitters are toggled; measuring flow rates through the irrigation systemas the irrigation system moves over the ground surface and as the wateremitters are toggled; comparing the measured flow rates to expected flowrates; creating a calibration map that reflects differences between themeasured flow rates and the expected flow rates at the determinedpositions; and calibrating operation of the irrigation system with thecalibration map by adjusting an operational aspect of the irrigationsystem to account for the differences between the measured flow ratesand the expected flow rates at the determined positions.

Another embodiment of the invention is an irrigation system comprising:a central pivot; a series of mobile towers each having wheels and amotor for driving the wheels; support structure for connecting themobile towers to each other and to the central pivot; a water-carryingconduit supported by the support structure; a plurality of wateremitters connected to the conduit for delivering water to a groundsurface; a valve for controlling water flow to the water emitters; and acontrol system for controlling operation of the mobile tower motors andthe valve so as to control the amount of water delivered to sections ofa field. The control system is programmed to: operate the mobile towersto move the irrigation system over the field; toggle the valve as theirrigation system moves over the ground surface; determine positions ofthe irrigation system as the irrigation system moves over the groundsurface and as the valve is toggled; measure fluid flow rates throughthe irrigation system as the irrigation system moves over the groundsurface and as the valve is toggled; compare the measured flow rates toexpected flow rates for the determined positions of the irrigationsystem; create a calibration map that reflects differences between themeasured flow rates and the expected flow rates at the determinedpositions; and calibrate operation of the irrigation system with thecalibration map by adjusting an operational aspect of the irrigationsystem to account for the differences between the measured flow ratesand the expected flow rates at the determined positions.

This summary is provided to introduce a selection of concepts in asimplified form that are further described in the detailed descriptionbelow. This summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter. Other aspectsand advantages of the present invention will be apparent from thefollowing detailed description of the embodiments and the accompanyingdrawing figures. For example, the principles of the present inventionare not limited to central pivot irrigation systems, but may beimplemented in other types of irrigation systems including linear moveirrigation systems.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

Embodiments of the present invention are described in detail below withreference to the attached drawing figures, wherein:

FIG. 1 is a perspective view of an exemplary central pivot irrigationsystem that may be used to implement aspects of the present invention.

FIG. 2 is a block diagram that depicts selected components of a controlsystem of the irrigation system.

FIG. 3 is a schematic plan view of a field that has been subdivided intoa number of wedge-shaped sections and showing the irrigation systemoperating in the field.

FIG. 4 is a schematic plan view of a field that has been subdivided intoa number of wedge-shaped sections with each section further divided intoa number of annulus sectors and showing the irrigation system operatingin the field.

FIG. 5 is a graphical representation of a calibration map that may beused to calibrate operation of the irrigation system.

FIG. 6 is a graphical representation of another calibration map that maybe used to calibrate operation of the irrigation system.

FIG. 7 is a flow diagram depicting exemplary steps in a method of thepresent invention or portions of a computer program of an embodiment ofthe present invention.

The drawing figures do not limit the present invention to the specificembodiments disclosed and described herein. The drawings are notnecessarily to scale, emphasis instead being placed upon clearlyillustrating the principles of the invention.

DETAILED DESCRIPTION

The following detailed description of embodiments of the inventionreferences the accompanying drawings. The embodiments are intended todescribe aspects of the invention in sufficient detail to enable thoseskilled in the art to practice the invention. Other embodiments can beutilized and changes can be made without departing from the scope of theclaims. The following detailed description is, therefore, not to betaken in a limiting sense. The scope of the present invention is definedonly by the appended claims, along with the full scope of equivalents towhich such claims are entitled.

In this description, references to “one embodiment”, “an embodiment”, or“embodiments” mean that the feature or features being referred to areincluded in at least one embodiment of the technology. Separatereferences to “one embodiment”, “an embodiment”, or “embodiments” inthis description do not necessarily refer to the same embodiment and arealso not mutually exclusive unless so stated and/or except as will bereadily apparent to those skilled in the art from the description. Forexample, a feature, structure, act, etc. described in one embodiment mayalso be included in other embodiments, but is not necessarily included.Thus, the present technology can include a variety of combinationsand/or integrations of the embodiments described herein.

Turning now to the drawing figures, and initially FIG. 1, an exemplaryirrigation system 10 on which principles of the present invention may beimplemented is illustrated. The illustrated irrigation system 10 is acentral pivot irrigation system, but it may also be a linear move orlateral type irrigation system or any other type of automated irrigationsystem. The illustrated irrigation system 10 broadly comprises a fixedcentral pivot 12, a main section 14 pivotally connected to the centralpivot, and a control system 100 (FIG. 2) for controlling operation ofthe irrigation system and for implementing the calibration features ofthe present invention.

The fixed central pivot 12 may be a tower or any other support structureabout which the main section 14 pivots. The central pivot has access toa well, water tank, or other source of water and may also be coupledwith a tank or other source of agricultural products to injectfertilizers, pesticides and/or other chemicals into the water forapplication during irrigation.

The main section 14 pivots or rotates about the central pivot 12 andincludes a number of mobile support towers 16A-D, the outermost 16D ofwhich is referred to herein as an end tower. The mobile towers areconnected to the fixed central pivot 12 and to one another by trusssections 18A-D or other supports to form a number of interconnectedspans. The illustrated irrigation system 10 has four mobile supporttowers, and thus four spans, however, it may comprise any number oftowers and spans without departing from the scope of the invention

The mobile towers have wheels 20A-D driven by drive motors 22A-D. Eachmotor 22A-D turns at least one of the wheels 22A-D through a drive shaftto move its mobile tower and thus the main section 14 in a circle orsemi-circle about the central pivot 12. The motors 22A-D may includeintegral or external relays so they may be turned on, off, and reversedby the control system 100 as described below. The motors may also haveseveral speeds or be equipped with variable speed drives.

Although not required, some or all of the towers 16A-D may be equippedwith steerable wheels pivoted about upright axes by suitable steeringmotors so that the towers can follow a predetermined track. U.S. Pat.No. 4,508,269 in the name of Davis et al. is hereby incorporated byreference in its entirety into the present specification for adisclosure of ground drive motors and steering motors associated with anirrigation machine. As is also well known, the drive motors for thetowers are controlled by a suitable safety system such that they may beslowed or completely shut down in the event of the detection of anadverse circumstance.

Each of the truss sections 18A-D carries or otherwise supports a conduitsection 24A-D or other fluid distribution mechanism that is connected influid communication with all other conduit sections and to a source offluids from the central pivot. A plurality of sprinkler heads, sprayguns, drop nozzles, or other water emitters 26A-P are spaced along theconduit sections 24A-D to apply water and/or other fluids to landunderneath the irrigation system.

At least one valve is disposed between the conduit sections 24A-D andthe water emitters 26A-P to control the flow of water through the wateremitters. In some embodiments, the irrigation system includes severalvalves, and each valve controls the flow of water through a single wateremitter such that each water emitter can be individually opened, closed,pulsed, etc. to emit any amount of water. In an embodiment illustratedin FIG. 2, the irrigation system 10 includes several valves 28A-D thateach control the flow of water through a group of water emitters suchthat the group of water emitters is controlled to emit a specific amountof water. For example, each span of the irrigation system may includefour water emitters, and one valve may control the water flow throughall four water emitters such that all of the water emitters on a spanoperate in unison. The valves may be magnetic latching solenoid valvesthat are normally biased to an off/closed state such that the valvesonly switch to an on/open state when powered, but they may be any typeof valve.

In accordance with one aspect of the invention, the irrigation system 10also includes at least one flow meter 30 (FIG. 2) that measures waterflow rates through the system. Outputs from the flow meter are providedto the control system 100 to calibrate the irrigation system asdescribed in more detail below. In one embodiment, a single flow metermeasures flow rates through the entire irrigation system and provides anindication of this aggregate flow rate to the control system. In otherembodiments, multiple flow meters provide flow-rate measurements throughdifferent portions of the irrigation system, such as through each spanof the irrigation system or even each water emitter. However, becauseequipping an irrigation system with multiple flow meters is costly andcomplicated, embodiments of the present invention permit calibration ofthe irrigation system with a single flow meter as discussed below.

Embodiments of the irrigation system may also include a pressureregulator for regulating the pressure of water through to the irrigationsystem. Pumps that provide water to the irrigation system may beconfigured to provide a minimum water pressure, and the pressureregulator then reduces the pump water pressure to a selected maximumpressure level such that the pumps and pressure regulator togetherprovide a relatively constant water pressure through the irrigationsystem. However, as described above and below, the water pressure of theirrigation system may still fluctuate as the irrigation system movesabout a field and/or over time as the pressure regulator ages.

The irrigation system 10 may also comprise other components such as anextension arm (also commonly referred to as a “swing arm” or “cornerarm”) pivotally connected to the free end of the main section and/or oneor more high pressure sprayers or end guns 32 mounted to the end tower16D or to the end of the extension arm. The end guns are activated atthe corners of a field or other designated areas to increase the amountof land that can be irrigated.

The control system 100 and its operation will now be described in moredetail. The control system 100 controls operation of the irrigationsystem and implements some of the calibration steps as described in moredetail below. The control system and can be implemented with hardware,software, firmware, or a combination thereof. One embodiment of thecontrol system 100 is illustrated in FIG. 2 and comprises a controlleror other computing device 102, memory 104, and a location-determiningcomponent 106. The control system 100 may also include conventionalinput devices such as knobs, buttons, switches, dials, etc.; inputs forreceiving programs and data from external devices; one or more displays;a cellular or other radio transceiver for wirelessly receiving andtransmitting data from and to remote devices; a bluetooth transceiver; awifi transceiver; and/or other electronic components.

The computing device 102 may comprise or include any number orcombination of processors, controllers, ASICs, computers or othercontrol circuitry. As illustrated, the computing device includes datainputs for receiving data from the flow-meter 30 and thelocation-determining component 106 and outputs connected to therelay-controlled valves 28A-B and the relay-controlled drive motors22A-D. The illustrated control system 100 is shown controlling fourdrive motors 22A-D and four valves 28A-D, but it may control any numberof motors and valves and other components of the irrigation system.

Some of the control functions described herein may be implemented withone or more computer programs executed by the computing device 100. Eachcomputer program comprises an ordered listing of executable instructionsfor implementing logical functions in the computing device 102 and canbe embodied in any computer-readable medium for use by or in connectionwith an instruction execution system, apparatus, or device, such as acomputer-based system, processor-containing system, or other system thatcan fetch the instructions from the instruction execution system,apparatus, or device, and execute the instructions. In the context ofthis application, a “computer-readable medium” can be any means that cancontain, store, communicate, propagate or transport the program for useby or in connection with the instruction execution system, apparatus, ordevice including, but not limited to, the memory 104. Thecomputer-readable medium can be, for example, but not limited to, anelectronic, magnetic, optical, electro-magnetic, infrared, orsemi-conductor system, apparatus, device, or propagation medium. Morespecific, although not inclusive, examples of the computer-readablemedium would include the following: an electrical connection having oneor more wires, a random access memory (RAM), a read-only memory (ROM),an erasable, programmable, read-only memory (EPROM or Flash memory), anoptical fiber, and a portable compact disk read-only memory (CDROM).

The memory 104 may be any electronic memory that can be accessed by thecomputing device 102 and operable for storing instructions or data. Thememory 104 may be integral with the computing device 102 or may beexternal memory accessible by the computing device. The memory may be asingle component or may be a combination of components that provide therequisite functionality. The memory may include various types ofvolatile or non-volatile memory such as flash memory, optical discs,magnetic storage devices, SRAM, DRAM, or other memory devices capable ofstoring data and instructions. The memory may communicate directly withthe computing device or may communicate over a bus or other mechanismthat facilitates direct or indirect communication. The memory mayoptionally be structured with a file system to provide organized accessto data existing thereon.

The location-determining component 106 may be any device capable ofdetermining positions of the irrigation system. The location-determiningcomponent may comprise, for example, an angle encoder positioned at thecentral pivot and the joint of each span of the irrigation system forsensing an angle between the central pivot 12 and the main section 14and between each span of the irrigation system. In some embodiments, theangle encoders may be incorporated in existing articulating jointspositioned between the spans so that the control system does not requireits own dedicated angle encoders. The location-determining component 106may also comprise one or more modified cam switches, proximity switches,optical encoders, potentiometers, light bar sensors, etc. at each spanjoint.

The location-determining component 106 may also be a global navigationsatellite system (GNSS) receiver such as a GPS receiver, Glonassreceiver, Galileo receiver, or compass system receiver attached to ornear one or more of the mobile towers and operable to receivenavigational signals from satellites to calculate positions of themobile towers as a function of the signals. Each GNSS receiver mayinclude one or more processors, controllers, or other computing devicesand memory for storing information accessed and/or generated by theprocessors or other computing devices. In some embodiments, a singleGNSS receiver receives satellite signals from separate antennas mountedto each mobile tower so that a receiver is not required at each tower.The GNSS receiver or receivers may be incorporated in the main controlsystem so that the control system does not require its own dedicatedGNSS receivers or may be stand-alone devices. Each GNSS receiver may becoupled with a patch antenna, helical antenna, or any other type ofantenna.

The location-determining component 106 may also comprise other type ofreceiving devices capable of receiving location information from atleast three transmitting locations and performing basic triangulationcalculations to determine the relative position of the receiving devicewith respect to the transmitting locations. For example, cellular towersor any customized transmitting radio frequency towers can be usedinstead of satellites. With such a configuration, any standard geometrictriangulation algorithm can be used to determine the exact location ofthe receiving unit.

Some or all of the components of the control system 100 may be enclosedin or supported on a weatherproof housing for protection from moisture,vibration, and impact. The housing may be positioned anywhere on or nearthe irrigation system and may be constructed from a suitable vibration-and impact-resistant material such as, for example, plastic, nylon,aluminum, or any combination thereof and may include one or moreappropriate gaskets or seals to make it substantially waterproof orresistant.

The above-described components of the control system 100 need not bephysically connected to one another since wireless communication amongthe various depicted components is permissible and intended to fallwithin the scope of the present invention. Thus, portions of the controlsystem 100 may be located remotely from the irrigation system and fromeach other.

Certain operational aspects of the control system 100 will now bedescribed. The control system 100 controls operational aspects of theirrigation system such as the speed and direction of the mobile towers,and hence the speed of the irrigation system, via control signalsprovided to the relays connected to the motors 22A-D of the mobiletowers 11A-D. Likewise, the control system 100 controls the water flowthrough the water emitters 26A-P via control signals provided to therelays connected to the valves 28A-D. The control system may alsocontrol other operational aspects such as a fertilizer application rate,a pesticide application rate, end gun operation, mobile tower direction(forward or reverse), and/or system start-up and/or shut-downprocedures.

The control system 100 may control some of the above-describedoperational aspects of the irrigation system in accordance with anirrigation plan (also sometimes referred to as a “sprinkler chart” or“watering plan”). An irrigation plan specifies how much water to applyto a field, and sometimes to different portions of a field, based onvarious different criteria such as the types of crops to be irrigated;the soil conditions in various parts of the field; the existence ofslopes, valleys, etc. in the field; the existence of roads, buildings,ponds, and boundaries that require no irrigations; crop growth cycles;etc. One or more irrigation plans may be created then stored in thememory 104 or otherwise be accessible by the computing device 102.

An exemplary irrigation plan will now be described with reference toFIG. 3, which shows a circular field 300 or portion of a field dividedinto a number of wedge-shaped sections 302-316. The field is showndivided into 8 equal-sized sections, but it may be divided into anynumber of sections of any size. The figure also depicts a four-spanirrigation system 10 operating in the field. Each of the wedge-shapedsections may require different amounts of irrigation for the reasonsdiscussed above.

An irrigation plan that corresponds to the field shown in FIG. 3indicates how much water is desired in each of the wedge-shaped sections302-316. For example, the irrigation plan may call for 10 G.P.M. insection 302, 20 G.P.M. in section 304, 0 G.P.M. in section 306, etc.This particular irrigation plan is likely for an irrigation system inwhich all the water emitters are turned on or off together (only onevalve for the entire irrigation system) because each wedge-shapedsection is not further sub-divided into smaller sections served by justsome of the water emitters.

Another exemplary irrigation plan will now be described with referenceto FIG. 4, which shows a circular field 400 or portion of a fielddivided into a number of wedge-shaped sections 402-416, with eachwedge-shaped section further sub-divided into a number of annulussectors identified by the letters A-D. The field is shown divided into 8equal-sized wedge-shaped sections, and each wedge is subdivided into 4annulus sectors, each corresponding to one span of the irrigation systemin a particular position in the field. However, the field may be dividedinto any number of sections and sectors of any size. At least some ofthe sections and/or annulus sectors may require different amounts ofirrigation for the reasons discussed above.

An irrigation plan that corresponds to the field shown in FIG. 4indicates how much water is desired in each of the annulus sectors. Thisirrigation plan is likely for an irrigation system that has a separatevalve for each span of the irrigation system such that the wateremitters on each span may be controlled separately from the wateremitters on other spans. For example, annulus sector 402B may receive adifferent amount of water than annulus sector 402D even through bothsectors are within the same wedge-shaped section 402.

The irrigation plans described above and/or other irrigation plans maybe stored in the memory 104 or may otherwise be accessible by thecomputing device 102. Each irrigation plan includes data that representsthe geographical boundaries of each of its sections and sectors and datathat represents the desired fluid amount or flow rate in the sectionsand sectors. For example, an irrigation plan may include data thatrepresents the boundaries or position of annulus section 402D and adesired water flow rate of 15 GPM in this sector. When the irrigationsystem is operating, the control system 100 adjusts the speed of themobile towers, the positions of the valves, and/or other operationalaspects of the irrigation system to achieve the amount of irrigationprescribed by one of the irrigation plans in the sections and sectors.

Those skilled in the art will appreciate that these are merely examplesof irrigation plans and that a nearly endless number of irrigation plansmay be created for the irrigation system 10. A more detailed explanationof irrigation plans is provided in U.S. Pat. No. 8,739,830, which isincorporated by reference into the present applicant in its entirety.

Even when controlled by an irrigation plan, the irrigation system 10 mayfail to deliver the prescribed amounts of water for the reasonsdiscussed above. The present invention solves this problem by providinga system and method for calibrating the irrigation system 10 to accountfor variations in flow rates caused by field elevation changes, pipefriction losses, water emitter nozzle wear, pressure-regulatorinaccuracies, and other factors. In general, the invention first createsa calibration map to assess and record the above-described flow ratevariations and then controls operation of the irrigation system 10 inaccordance with the calibration map.

To create a calibration map, actual flow rates through the irrigationsystem 10, or portions of the irrigation system, are periodically orcontinuously measured and recorded as the irrigation system 10 movesacross a field. These measured flow rates are then compared to expectedflow rates through the irrigation system, or portions of the irrigationsystem, based on the original design or configuration of the irrigationsystem. Correction factors that account for the differences between themeasured flow rates and the expected flow rates are then created fordifferent portions or sections of the field. For example, if themeasured flow rate in a first section is 5% less than expected, acorrection factor of +5% is assigned to that section to indicate 5% morewater is required in that section. Similarly, if the measured flow ratein a second section is 10% more than expected, a correction factor of−10% is assigned to that section to indicate 10% less water is requiredin that section. The correction factors and geographic coordinates orother positional information for the corresponding field sections arethen stored in the calibration map.

The calibration map may be created while the irrigation system isoperating in a calibration mode or “on-the-fly” while the irrigationsystem is irrigating a field. The calibration map may be created whenthe irrigation system is first placed into service and may beperiodically or continuously updated to account for changing conditionssuch as degradation of the valves, water emitters, pressure regulatorand/or other components of the irrigation system.

Creation of exemplary calibration maps will now be described in moredetail with reference to the exemplary irrigation plans described above.Although each calibration map may correspond to a particular irrigationplan, the calibration maps are not necessarily linked to particularirrigation plans and may be used to calibrate any number of irrigationplans or even an irrigation system that is not operating under thedirection of an irrigation plan.

A first exemplary calibration map is graphically represented in FIG. 5and may correspond to the field represented in FIG. 3 and the irrigationplan created for this field. As depicted, the calibration map hascorrection factors for each pie-shaped section 302-316 of the irrigationplan. The correction factors are shown as percentages but may be inother forms such as fractions, decimals, or other data. This calibrationmap corresponds to an irrigation system that does not control individualwater emitters or banks of water emitters but instead controls all ofthe water emitters with a single valve.

The calibration map represented in FIG. 5 is created by measuring andrecording actual flow rates through the irrigation system, or portionsof the irrigation system, while it operates in each of the sections302-316. These measured flow rates are then compared to expected flowrates through the irrigation system, or portions of the irrigationsystem, for the same sections. Differences between the measured flowrates and the expected flow rates for the sections are then calculatedto create correction factors for each section of the field. For example,section 302 shows a correction factor of +10%, which indicates themeasured flow rates for section 302 are 10% below the expected flowrates and therefore 10% more water is required for that section.Similarly, section 310 shows a correction factor of −15%, whichindicates the measured flow rates for that section are 15% above theexpected flow rates and therefore 15% less water is required for thatsection.

FIG. 5 is just a graphical representation of the first calibration map.In actual implementation, the calibration map is likely stored as atable, database, or other data structure, with data corresponding to thegeographical coordinates of the sections 302-316 and the correctionfactors for each section.

A second exemplary calibration map is graphically represented in FIG. 6and may correspond to the field represented in FIG. 4 and the irrigationplan created for this field. The calibration map has correction factorsfor at least some of the annulus sectors, and preferably all thesectors, but the figure only includes a few representative correctionfactors. This calibration map likely corresponds to an irrigation systemthat has a separate valve for each span of the irrigation system suchthat the water emitters on each span may be controlled separately fromthe water emitters on other spans.

The second calibration map is created in a similar manner as the firstcalibration map but requires extra steps to account for the annulussectors. This calibration map is created by measuring and recordingactual flow rates through each span of the irrigation system while itoperates. During a calibration pass, the control system toggles orotherwise controls individual water emitters, or banks of wateremitters, on and off by operating the valves 28A-D. The control systemdetermines how much water is actually being emitted from individualwater emitters, or banks of water emitters, by comparing changes in theoverall flow rate through the irrigation system as the water emittersare toggled. For example, the control system may close the wateremitters on the outermost span of the irrigation system, but leave allother water emitters fully open, and then note how much the total waterflow through the irrigation system dropped. Because the pressureregulator maintains a relatively constant water pressure in theirrigation system even as valves are opened and closed, the water flowreduction approximates the amount of water flow through the wateremitters on the outermost span of the irrigation system when they arefully open. These steps may be repeated for every group of wateremitters, and even for individual water emitters, for each annulussector of the field.

These measured flow rates are then compared to expected flow ratesthrough the spans for the sectors. Differences between the measured flowrates and the expected flow rates for the sectors are then determined tocreate correction factors for each annulus sector of the field. Forexample, sector 402D shows a correction factor of +10%, which indicatesthe measured flow rates for that sector are 10% below the expected flowrates for that sector and therefore 10% more water is required for thatsector. Similarly, sector 408C shows a correction factor of −15%, whichindicates the actual flow rates for that sector are 15% above theexpected flow rates and therefore 15% less water is required for thatsector.

Once a calibration map is created, the control system 100 consults thecalibration map during operation of the irrigation system to adjust atleast one operational aspect of the irrigation system in accordance withthe correction factors. For example, if an irrigation plan or an initialsetting of the irrigation system calls for 10 gallons per minute(G.P.M.) of water in a section or sector of the field, but thecalibration map indicates a +10% correction factor for the section orsector, the control system adjusts an operational aspect of theirrigation system so as to apply 10% more water than it would havewithout the calibration map. The operational aspect that is adjusted maybe the speed of the irrigation system's mobile towers, a duty cycle ofthe irrigation system's water emitters, a water flow rate of individualwater emitters or banks of water emitters, or anything else thatcontrols the rate of fluid flow of the irrigation system to adjust waterflow rates in accordance with the correction factors. For example, thecontrol system may operate the mobile towers 10% slower than called forby the irrigation plan or the initial setting of the irrigation systemso as to apply 10% more water.

The above-described calibration maps can also be used to detect faultsin an irrigation system such as leaks, valves stuck open, end guns stuckopen, abnormally high system water pressures, blocked water emitternozzles, valves stuck closed, end guns stuck closed, and abnormally lowsystem water pressures. For example, if a calibration map indicatesmeasured water flow rates are much higher than expected for multiplesections or sectors of a field, this may indicate a leak, valve stuckopen, or end gun stuck open. By successively toggling different valvesor banks of valves, the control system can isolate which water emittersor banks of water emitters that are stuck open or closed.

When a calibration map is updated, the control system may compare themost current version of the calibration map to one or more previousversions of the calibration map to detect changes in the correctionfactors. These changes, if gradual, may indicate normal and expectedwater flow variations, but if significant, may indicate problems such asstuck valves, leaks, and/or other defects.

The flow chart of FIG. 7 shows the functionality and operation of anexemplary method 700 of the present technology. Some of the blocks ofthe flow chart may represent a step in the method 700 and/or a modulesection or portion of code of computer programs the operate the controlsystem 100. In some alternative implementations, the functions noted inthe various blocks may occur out of the order depicted in FIG. 7. Forexample, two blocks shown in succession in FIG. 7 may in fact beexecuted substantially concurrently, or the block may sometimes beexecuted in the reverse order depending upon the functionality involved.

The method 700 begins in step 702 where the control system operates themobile towers to move the irrigation system over a ground surface. Thecontrol system may operate the mobile towers and water emitters inaccordance with an irrigation plan or initial settings of the irrigationsystem.

In step 704, the control system receives position or orientationinformation for the mobile towers 16A-D. The position or orientationinformation may be obtained from the location-determining component 106or a similar device. This step, and all other steps of the method, maybe performed in a different order. For example, the position of theirrigation system may be determined after and/or during steps 706 and708.

In step 706, the control system 100 toggles the water emitters as theirrigation system moves over the ground surface. In step 708, thecontrol system 100 measures flow rates through the irrigation system asthe irrigation system moves over the ground surface and as the wateremitters are toggled. Steps 706 and 708 allow the control system todetermine actual flow rates through specific water emitters or banks ofwater emitters as described above. The toggling step is not required foran irrigation system with a single valve that controls water delivery toall the water emitters.

In step 710, the control system 100 compares the measured flow rates toexpected flow rates. This step and other steps may be repeated for everysection and sector of the field as described above.

In step 712, the control system 100 creates a calibration map thatreflects differences between the measured flow rates and the expectedflow rates in the sections and sectors. As discussed above, thecalibration map includes correction factors for different sectionsand/or sectors. These correction factors account for the differencesbetween the measured flow rates and the expected flow rates in thesections or sectors and are used to adjust operational aspects of theirrigation system.

In step 714, the control system 100 calibrates operation of theirrigation system 10 with the calibration map by adjusting at least oneoperational aspect of the irrigation system to account for thedifferences between the measured flow rates and the expected flow rates.The operational aspects of the irrigation system that can be adjustedmay be a speed of the mobile towers, a duty cycle of the water emitters,a water flow rate of the water emitters, or anything else that controlsthe rate of fluid flow of the irrigation system.

Some of the above-described steps may be performed by the control system100 and/or an external computing device not located on the irrigationsystem. The external computing device may communicate with the controlsystem 100 or directly with the drive motors 22A-D and/or the valves28A-D via wireless communication channels.

Although the invention has been described with reference to theembodiments illustrated in the attached drawing figures, it is notedthat equivalents may be employed and substitutions made herein withoutdeparting from the scope of the invention as recited in the claims. Forexample, the principles of the present invention are not limited to theillustrated central pivot irrigation systems but may be implemented inany type of irrigation system including linear move irrigation systems.

Having thus described the preferred embodiment of the invention, what isclaimed as new and desired to be protected by Letters Patent includesthe following:
 1. A method of calibrating an irrigation system having aplurality of mobile towers and a plurality of water emitters supportedby the mobile towers, the method comprising: operating the mobile towersin accordance with an irrigation plan to move the irrigation system overa ground surface and to apply selected and different amounts of fluidsto a plurality of sections of the ground surface; determining positionsof the irrigation system as it moves; measuring flow rates through theirrigation system for each of the sections as the irrigation systemmoves over the ground surface; comparing the measured flow rates toexpected flow rates for each of the sections; creating a calibration mapthat reflects differences between the measured flow rates and theexpected flow rates for each of the sections, the calibration mapincluding a separate correction factor for each of the sections, whereineach of the correction factors accounts for differences between themeasured flow rate and the expected flow rate for its respective sectionand not any of the other sections; and calibrating operation of theirrigation system with the calibration map by adjusting an operationalaspect of the irrigation system for each of the sections in accordancewith the separate correction factors for the sections to account for thedifferences between the measured flow rates and the expected flow ratesfor each of the sections so that each of the sections is calibratedindependently.
 2. The method as set forth in claim 1, wherein theoperational aspect of the irrigation system is selected from the groupconsisting of a speed of the mobile towers, a duty cycle of the wateremitters, and a water flow rate of the water emitters.
 3. The method asset forth in claim 1, wherein the steps are performed during acalibration run of the irrigation system or while the irrigation systemis irrigating the ground surface.
 4. The method as set forth in claim 1,further including the step of toggling the water emitters as theirrigation system moves over the ground surface.
 5. The method as setforth in claim 4, wherein the toggling step comprises turning a set ofthe water emitters off, and wherein the measuring step determines themeasured flow rates for the set of water emitters by measuring areduction in flow rates through the irrigation system when the set ofwater emitters are turned off.
 6. The method as set forth in claim 5,wherein the measuring step is performed with a single flow rate sensorthat senses flow rates through the entire irrigation system.
 7. A methodof calibrating an irrigation system having a plurality of mobile towersand a plurality of water emitters supported by the mobile towers, themethod comprising: operating the mobile towers in accordance with anirrigation plan to move the irrigation system over a ground surface andto apply selected amounts of fluids to a plurality of sections of theground surface; toggling the water emitters as the irrigation systemmoves over the ground surface; determining positions of the irrigationsystem as the irrigation system moves over the ground surface and as thewater emitters are toggled to determine which section is beingtraversed; measuring flow rates through the irrigation system for eachof the sections as the irrigation system moves over the ground surfaceand as the water emitters are toggled; comparing the measured flow ratesto expected flow rates for each of the sections; creating a calibrationmap that reflects differences between the measured flow rates and theexpected flow rates for each of the sections, the calibration mapincluding a separate correction factor for each of the sections, whereineach of the correction factors accounts for differences between themeasured flow rate and the expected flow rate for its respective sectionand not any of the other sections; and calibrating operation of theirrigation system with the calibration map by adjusting an operationalaspect of the irrigation system for each of the sections in accordancewith the separate correction factors for the sections to account for thedifferences between the measured flow rates and the expected flow ratesfor each of the sections.
 8. The method as set forth in claim 7, whereinthe operational aspect of the irrigation system is selected from thegroup consisting of a speed of the mobile towers, a duty cycle of thewater emitters, and a water flow rate of the water emitters.
 9. Themethod as set forth in claim 7, wherein the toggling step comprisesturning a set of the water emitters off while leaving other wateremitters on.
 10. The method as set forth in claim 7, wherein themeasuring step measures a flow rate reduction as the set of wateremitters are turned off, and wherein the comparing step compares theflow rate reduction to expected flow rates for the set of wateremitters, and wherein the calibration map reflects differences betweenthe measured flow rate reduction and the expected flow rates for the setof water emitters.
 11. An irrigation system comprising: a series ofmobile towers each having wheels and a motor for driving the wheels;support structure for connecting the mobile towers to each other; awater-carrying conduit supported by the support structure; a pluralityof water emitters connected to the conduit for delivering water to aground surface; a plurality of valves for controlling water flow to thewater emitters; and a control system for controlling operation of themobile tower motors and the valves, the control system programmed to:operate the mobile towers in accordance with an irrigation plan to movethe irrigation system over a ground surface and to apply selectedamounts of fluids to a plurality of sections of the ground surface;toggle the valves as the irrigation system moves over the groundsurface; determine positions of the irrigation system as the irrigationsystem moves over the ground surface and as the valves are toggled todetermine which section is being traversed; measure fluid flow ratesthrough the irrigation system for each of the sections as the irrigationsystem moves over the ground surface and as the valves are toggled;compare the measured flow rates to expected flow rates for thedetermined positions of the irrigation system for each of the sections;create a calibration map that reflects differences between the measuredflow rates and the expected flow rates for each of the sections, thecalibration map including a separate correction factor for each of thesections, wherein each of the correction factors accounts fordifferences between the measured flow rate and the expected flow ratefor its respective section and not any of the other sections; andcalibrate operation of the irrigation system with the calibration map byadjusting an operational aspect of the irrigation system for each of thesections in accordance with the separate correction factors for thesections to account for the differences between the measured flow ratesand the expected flow rates for each of the sections.
 12. The irrigationsystem as set forth in claim 11, wherein the operational aspect of theirrigation system is selected from the group consisting of a speed ofthe mobile towers, a duty cycle of the water emitters, and a water flowrate of the water emitters.
 13. The irrigation system as set forth inclaim 11, further comprising a central pivot to which the supportstructure is attached.
 14. The irrigation system as set forth in claim11, wherein the control system is positioned on the irrigation system.15. The irrigation system as set forth in claim 11, wherein the controlsystem is positioned remotely from the irrigation system.
 16. Theirrigation system as set forth in claim 11, wherein some components ofthe control system are positioned on the irrigation system and othercomponents of the control system are positioned remotely from theirrigation system.